你的命令可以簡化一下

>>x=0:0.01:pi;

>>y=cos(x);

>>z=sin(x);

>>plot(x,y,x,z)

>>legend("y=cos(x)","z=sin(x)")

這樣顏色就不一樣

你的x是向量，y是標量。不同維。預設繪製的圖實際上有x元素個數個圖。將x,y維數統一就行了

p=0.99;

k=0:1000;

geomSeries=p.^k;

G=1/(1-p);

x=0:max(k);

y=G*ones(size(x,1),size(x,2));

plot(x,y,"r",x,cumsum(geomSeries),"b");

xlabel("index");

ylabel("Sum");

title("Convergence of geometric with p=0.99");

legend("Infinite sum","Finite sum","3");

ylim([0,120]);